1. Field of the Invention
The present invention relates to a photolithographic apparatus and operating method thereof, and more particularly, to a method of correcting mask pattern and correcting apparatus thereof.
2. Description of the Related Art
In recent years, the trend in the development of semiconductor is miniaturization of circuit devices. Among the processes used in semiconductor production, photolithographic process plays a very important role. Critical dimensions (CD) concerning semiconductor device structures, such as patterning various thin films, are dependent on the photolithographic process, which also determine the development of photolithographic technology. Thus, the accuracy of a photomask pattern is very crucial. If the pattern on the photomask is inaccurate, an inaccurate pattern will be transferred. Hence, the tolerance of the critical dimension on the chip can be affected and the resolution of the exposure can be reduced.
In a general photomask fabrication, the circuit layout pattern (the original mask layout pattern 100 in FIG. 1 ) of an integrated circuit is stored in magnetic tapes through a computer-aided design (CAD) system. Then, the designed circuit layout pattern is exposed to a glass plate or quartz plate coated photosensitive material. Next, the exposed photosensitive material is chemically developed and etched to form a mask with the circuit layout pattern. The conventional method of correcting the pattern on the corner region of the mask includes: using the software program within the mask writer to compute the size of the exposure compensating value when the mask writer is used to carry out the exposure. However, the exposure compensated mask pattern will still produce some corner rounding effect after the steps of chemical development and etching. In general, there are two major types of photo-exposure processes: one uses a laser beam while another uses an electron beam. In the laser beam exposure process, a laser beam is used to write out the pattern. One disadvantage of the laser beam method is the susceptibility of the pattern on the mask to the corner rounding effect as shown in the distorted pattern 102 in FIG. 1. The accuracy of the pattern and the process window are seriously affected especially when the dimension of the circuit design pattern is small.
In the electronic beam (e-beam) process, an electron beam is used to write out the pattern. The corner rounding effect on the pattern of the mask is less serious and the method has less effect on the process window of the photolithographic process. However, using an electronic beam to write out the pattern has a throughput significantly lower than using a laser beam. Furthermore, the cost of producing a mask using the electronic beam method is more than 5 times the cost of producing the same mask using the laser beam method.
In U.S. Pat. No. 6,792,592, a method for forming an accurate pattern on a photomask is disclosed. The method performs a selection of the appropriate writer properties and then uses the selected writer properties to choose the mask writer for the job. However, the method in the disclosure limits the formation of the pattern on the mask through the selected mask writer. Hence, the method can hardly solve the aforementioned problem.